The human brain is an exceedingly complex processing system, which integrates continual streams of incoming sensory input data with stored memories, uses the input data and memories in complex decision processes at both conscious and unconscious levels, and on the basis of these processes generates observable behaviors by activation of its motor or movement control pathways and the muscles which these innervate.
In the United States, approximately 12,000 people each year suffer some form of spinal cord injury (SCI), with over 275,000 people chronically paralyzed from SCI. There are two general types of SCI: complete and incomplete lesions. Complete lesions leave the patient with no motor, sensory, or autonomic function below the level of the lesion. Transection of the spinal cord is the most obvious cause of a complete lesion. The level of the injury in the spinal cord determines exactly what function will be lost, as the spinal nerves that exit the cord below this are absolutely unable to transmit signals to or from the brain. Incomplete lesions can take a variety of forms, and depending on the nature of the trauma, a range of motor and sensory abilities may be present.
Non-traumatic pathologies such as stroke and Parkinson's disease are also often characterized by a patient's inability to successfully translate a desire into the appropriate motions of the relevant limbs. Central nervous system pathologies are often responsible for varying levels of paralysis, which cause immense suffering in the affected population.
Rehabilitation efforts for these patients usually focus on teaching means for using still-functioning limbs to carry out desired tasks, while trying, when possible, to recover some function in the affected limbs. In addition, a range of technologically advanced and expensive devices have been built and tested on patients with limited success. Amongst these are muscle-stimulation devices, which include electrodes that are mounted on a patient's muscles in a paralyzed limb. In response to a command, the electrodes drive current into the muscles, causing the contraction thereof. The resultant motion of the limb is typically rough, and the unnatural stimulation protocols often leave the patient's muscles tired, even after performing only a small number of tasks.
U.S. Pat. Nos. 5,178,161; 5,314,495 and 4,632,116 provide the use of microelectrodes to interface between control electronics and human nerves.
U.S. Pat. No. 4,649,936 discloses an electrode cuff for placement around a nerve trunk, for generation of unidirectional propagating action potentials.
U.S. Pat. No. 4,019,518 provides methods for using an electrical stimulation system to selectively stimulate portions of the body.
U.S. Pat. Nos. 5,776,171; 5,954,758 and 6,026,328 disclose methods and devices for stimulating muscles of limbs of the body, so as to achieve motion and control of the limbs in patients with central nervous system disabilities. Limb motions in each limb are commanded by external means and communicated via radio waves to an apparatus implanted in the limb. Actual motion of the limb is monitored and compared to the commanded motion with the goal of attaining real-time control of the limb.
U.S. Pat. No. 5,748,845 provides a device for controlling limbs of patients with central nervous system disabilities. The activity of a healthy muscle is sensed, analyzed, and used to determine input parameters to a control system of the device. Both external mechanical apparatus and direct electrical stimulation of muscle tissue are described as means for inducing movement of the disabled limb.
Other methods and devices for sensing muscular contractions and for applying muscular stimulation are provided by U.S. Pat. Nos. 6,091,977; 6,104,960; 6,086,525; 4,926,865; 4,392,496 and 6,146,335.
U.S. Pat. No. 6,119,516 discloses a biofeedback system, optionally including a piezoelectric element, which measures the motions of joints in the body. U.S. Pat. No. 5,069,680 provides the use of a piezoelectric crystal as a muscle activity sensor. U.S. Pat. Nos. 4,602,624 and 5,505,201 disclose techniques for making implantable electrodes. U.S. patent application Ser. No. 20020161415 further provides a plurality of electrodes, which are adapted to be placed in a vicinity of a motor nerve that innervates the skeletal muscle.
Despite these advances there remains a need for a means to communicate with the regions of the brain via an external interface which is plastically adaptive, sensitive, and responsive to the subtleties of nerve transmission.